This bird has a certain Caspian feel to it, facial expression, small head, long neck, snouty face, long wings, long pale legs, hanging rear belly and strikingly white tail coverts and the pale underwing etc but there are a few features which lend the bird away from being a pure blood.
The tertials although very dark show a lot of white at the tips and the fringes, the bill pattern is suggestive more of a Herring Gull at 2nd winter age rather than of a Casp, the upperparts are to blue-grey (quite advanced), The extent of the barring on the upper-tail and under-tail coverts is extensive and bold.
The greater coverts are uniformly dark across the wing creating a constrasting dark panel when compared with the pale fringed median and lesser coverts. The white head certainly contrasts with the lower hind neck streaking.
On the spread wing there is little contrast across the primaries, the inners do not form an obious paler panel, and there is a small mirror to P10.
I've never seen a pure Caspian look like this, nor a Herring Gull for that matter, so I believe this bird is likely to a hybrid CaspianxHerring Gull.
